Visuospatial orientation is the knowledge of one's location that allows navigation through the environment. It relies on optic flow to monitor the path of self-movement and object vision to monitor relative position. If optic flow and object cues for spatial orientation are processed separately in dorsal and ventral visual areas, they might function separately and interact differently with memory, motor control, and vestibular systems. I will assess the independence of optic flow and object vision in visuospatial processing by testing three specific hypotheses: 1) That object vision dominates heading memory because of strong connections between ventral visual areas and the hippocampus. 2) That optic flow dominates heading motor control because of strong connections between dorsal visual areas and motor centers. 3) That real movement interacts more with optic flow than object cues because cortical vestibular centers are more closely connected to dorsal visual areas. I will test these hypotheses in normal subjects by presenting optic flow and object stimuli as cues about the heading of self-movement in three experiments: 1) pointing to a remembered heading, 2) manual steering toward a target heading, and 3) heading perception during real translational movement. My goals are to characterize the perceptual mechanisms of visuospatial orientation, relate cognitive function to neural organization, and examine the applicability of the dual pathways view to visuospatial information processing. I will use the same approach in a parallel analysis of visuospatial disorientation, a common and debilitating aspect of Alzheimer's disease (AD). These studies will test whether impaired optic flow perception in AD is separate from deficits in object vision by identifying double dissociations between impaired cue use in visuospatial tasks. My goal is to integrate visual psychophysics and the analysis of visuospatial deficits to develop the requisite scientific foundation for clinical studies of visuospatial disorientation in AD.